In recent years, the performance sought from tires has become of a higher order due to various techniques. As one example, the decrease in the rolling resistance of the tire is being strongly sought due to the needs of the market for greater fuel efficiency. As the technique for reducing the rolling resistance, there is the art of modifying the ends of rubber molecules with various functional groups to improve the dispersability of a filler in the rubber to thereby improve the fuel efficiency. However, modifying the ends of rubber molecules and obtaining the maximum effect of the same requires modification of many end groups. As a result, the molecular weight of the rubber is decreased. When low molecular weight end-modified rubber is used, in particular when silica is used, as a filler, a long period of mixing is required for sufficient reaction and filler dispersion, but, in this case, there is the problem that the rubber molecules are increasingly cut to thereby cause the decrease in the viscosity.
To solve these problems, if it is possible to modify the main chains of rubber during mixing, it would be possible to increase the interaction between rubber and fillers, without causing the decrease in the molecular weight and would be possible to obtain a rubber composition capable of satisfying the desired tire performance. Accordingly, in the present invention, a specific compounding agent (i.e., 4,4′-oxybis(benzenesulfonylazide)) is used as the main chain modifying agent to thereby successfully obtain a rubber composition for a tire capable of increasing the interaction between rubber and fillers. Thus, the rubber composition for a tire having excellent fuel efficiency can be obtained.
In the past, it has been proposed to use the 4,4′-oxybis(benzenesulfonylazide), as a curing agent, to obtain an elastomer composition having an excellent ozone resistance, etc. (see, for example, Japanese Patent Publication No. 6-11815B and Japanese Patent Publication No. 7-5798B), to use this, as a foam agent/cross-linking agent, to obtain a sponge-like rubber composition for a molding die, which does not generate clouding or polluting the contacted members (see, for example, Japanese Patent Publication No. 8-134248A), etc. However, there has been no known document which, like the present invention, uses this as a main chain modifying agent of rubber so as to obtain a rubber composition for a tire having an excellent fuel efficiency.